1. Field of the Invention
This invention relates to fluoran leuco dyes. It more particularly relates to fluoran leuco dyes containing a phenylenediamine moiety and processes for manufacturing such fluoran leuco dyes.
Fluoran leuco dyes containing a phenylenediamine moiety are useful as neutral color formers in applications such as heat sensitive and pressure sensitive recording materials. These normally colorless or light colored dyes express a color form when contacted with acidic or alkaline developers. Advantageously these materials can express a neutral or blackish hue.
2. Description of the Related Art
Fluoran leuco dyes for forming recording materials are described in Obitsu et al. U.S. Pat. Nos. 4,954,631 and 4,826,806.
Obitsu et al. teaches a synthesis involving reacting an aminophenol derivative with a keto acid such as a benzoic acid derivative in the presence of sulfuric acid.
Condensing a keto acid and a diphenylamine in sulfuric acid to produce a fluoran dye containing a phenylenediamine moiety typically results in poor yields. This makes the material costly to manufacture thereby limiting commercial acceptability. As a result, these materials are not believed to have been widely adopted.
The keto acid and diphenylamine condensation in sulfuric acid route to produce the fluoran leuco dyes is susceptible to various side reactions resulting in poor yield of the product.
In U.S. Pat. No. 4,954,631 Obitsu for example illustrates reacting one gram of 2-(5′-chloro-2′-hydroxy-4′-methyl) benzoylbenzoic acid with one gram of 3-methoxy-4′-(4″-phenylamino)phenylamino)diphenylamine and in the end isolating only 0.7 gram of 3-[4′-(4″-phenylaminophenylamino)-phenylamino]-6-methyl-7-chlorofluoran.
It would be desirable and of commercial significance if fluoran leuco dyes containing a phenylenediamine moiety can be made in higher yield with fewer side reactions and fewer unwanted by-products.
It is an object of the present invention to disclose an improved process for manufacture of fluoran leuco dyes containing a phenylenediamine moiety. The process of the invention has fewer side reactions, fewer by-products and higher yield.